Twin Studies Dissection Of Genetic Factors From Environmental Influences

Familial aggregation may be due to genetic or shared environmental factors. Twin studies can be used to estimate the contribution of inheritance to the familial aggregation of a trait or disease by comparing the similarities (concordance rate) of a trait or disease in monozygotic (MZ, genetically identical) and dizygotic (DZ, sharing on average 50% of genetic material) twins. In a registry of 4840 male twin pairs in Sweden, 458 cases of prostate cancer were identified. There were 16 concordant pairs among 1649 MZ twin pairs (1%) but only six concordant pairs among 2983 DZ twin pairs (0.2%). The greater concordance rate seen in MZ twins compared to DZ twins is attributed to a greater degree of shared genes.2 A second twin study, conducted in the United States, showed similar results.4 Among 1009 twin pairs identified from a national twin registry, a significantly higher concordance rate was observed among MZ twins (27.1%) compared to DZ twins (7.1%). It was estimated that genetic influences account for approximately 57% and environmental influences for 43% of the variability in twin liability for prostate cancer. In the twin study conducted by Lichtenstein et al.,6 a 21% concordance rate was found in MZ twins but only a 6% concordance rate in DZ twins. It was estimated that 42% [95% confidence interval (CI) = 29%-50%) of prostate cancer risk was due to heritable factors, and this genetic contribution was the highest among all neoplasms studied.

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